Manufacture of thermoplastic resinous materials



MANUFACTURE 0F THERMOPLASTIC RSOUS MATER-IALS Filed Feb. 17, i955.

INVENTOR Pn rs1-mlb val d, E EHT Evyk ATTORNEY Patented Mar. 24, 1936 UNITED STATES PATENT oFFlcE F THERMOPLASTIC yRESINOUS MATERIALS Archibald Renfrew, simlock, scotland, assigner f t0 Imperial Chemical Industries Limited, a corporation of Great Britain I Application February 17, 1933, Serial No.`657,302

In Great Britain February' 29, 1932 4 claims.

This invention relates tothe manufacture of thermoplastic resinous materials, e. g. polymerized vinyl acetate or the like, and in particular to amethod for deaerating or removing bubbles 5 from plates, blocks or other compact masses of such materials. Y

While it might be thought that the removal A of bubbles could be accomplished by heating the material to such a temperature that it becomes liquid, or atleast sufliciently uid for the bubbles to rise of themselves Within a reasonable time, it is found in practice this can seldom be.

The drawing accompanying this application is generally illustrative of a sheet of glass containing an inner layer of thermoplastic material prepared in accordance with the invention.

According to the inventiomwe deaerate a bubbly compact mass of thermoplastic resinous material by subjecting it under pressure in asuitable shaped container, for a more or less extended period of time, to a temperature sumc'ient to vent for such vlatile matter. Water; alcohol, oils, for instance, vegetable oils such as castor` oil, or mineral oils such as hydrocarbon oilare examples of inert liquids which may be used in.' particular lcases, such as that of polymerized vinyl acetate. 1- .4 l

In the preferred method of carrying out the invention we place the mass of thermoplastic material in an openivessel of suitable shape, and cover it with the inert liquid: We then trans- .fer the vessel and contents to an autoclave and subject them to a moderately elevated tempera ture, e. g. 50200 C., and high pressure, e. g.,

`. 2-.50 atmospheres. The' temperature, preasxu'e soften the mass, but not so high as to cause its (on. zoos-2) l and time of treatment dependen the nature of the material but may be varied within wide lim-v its. In the case of vinyl acetate polymers a teme y .perature of 120 C. should not be exceeded.

The invention is illustrated by the following 5 example. to which however, it is not limited.

i Example A bubbly block of polymerized vinylacetate, of the kindinsoluble in absolute alcohol, is placed in a tin vessel and is covered with a layer of hydrocarbon oil and heated in an autoclave to C. under apressure of 400 lbs. per square inch. When this temperature is attained, heating is discontinued and the temperature is allowed to fall to 20*f C. overnight, and the pressure lis then released. The bubbles are found to have left the interior of the block and either to have disappeared or to have risen to the surface of the block.- The hydrocarbon oil may be replaced by water, absolute alcohol or castor oil.

While the above example specifically refers to polymerized vinyl acetate, it is understood that other plastic materials may be employed and that their use is contemplated; Among such mate- 25 rials lare the vinyl compound resins, methyl methacrylate resin and phenol-formaldehyde cast typey resin. l n .l

The -thermoplastic material treated according l to the invention may be substantially free from 30 foreign matter, or it mayv contain one or more1 oi the usual softening agents (e. g. dibutyl phthalate) or fillers (e. g. barytes) or other com- I mon adjuvants'.

, ments of this'invention may be made without departing from the spirit and scope ithereof, it is to be understood'that I do not v`limit'myself to the specific' embodiments thereof except as deined in thefollowing claims:

I blaim: 1. A method of removing bubblesfrom4 already formed thermo-plastic material which comprises subjecting the material asa unit, without the addition of solvent thereto, in a bath of an inert 45. liquid, said bath coveringl any free surface of the material, to a pressure, to a temperature and for a period oiltime suiiicient to soften the mass but insufficient t'o cause decomposition or loss of thermoplasticity,

2. The method accordin to claim 1 wherein the material isa vinyl com und resin. 3. The method according to claim 1 wherein the `material is polymerized vinyl acetate.-

4. The method according to claim 1 wherein. 55 the material is a .methyl methacrylate resin. ARCHIBALD RENFREW,

As many apparently widely diiferentvenibodi- 35' 

